Storage and stacking devices used to store and stack various parts, for example letters, newspapers, magazines, folded sheets, cards, film bags and like, are known. They are used primarily in the distribution and sorting areas of the post office and similar operations. Known letter sorting and distributing systems are very limited in the range of shipments which they can process. A majority of the shipments encountered today in the post office are classified as "not machine-handleable" because no distribution systems exist for these types of shipments. Problems occur in picking, sorting, transporting, and stacking different shipments.
JP-PS 57-48557 teaches a device for stacking and storing postal shipments. It consists of a circular endless belt on which individual boxes are arranged in which letters or the like are placed by means of a suitable feed device. These pieces are placed on a stack conveyor located beneath the feed device. A stack support is located on this stack carrier. The pieces of mail are placed in the boxes by the feed device. To keep them from tipping over and guide them correctly, guidance of the letter is necessary; this is provided by a feed device since otherwise there is a danger that the letter will either fall out of the box or onto the belt or get jammed between the belt and the box or fall backward.
It is also necessary to provide a roller which ensures that the corresponding travel of the belt will keep the letters or pieces of mail that are added in a vertical position. It is only possible with this vertical position for the pieces of mail to be added to the forming stack to be vertical at the outset. The letters are added to the stack in such a way that the box crosses through the stack carrier.
However, to keep it from cutting into the already stacked pieces of mail, the stack support must move backward so that the entire stack can be moved by the moving box and by the incoming mail so that the box has sufficient room to pass through the stack carrier. This causes the stack which is already on the stack carrier to fall back or makes it sufficiently unstable that the individual pieces of mail are displaced with respect to one another and against the support as well as against the other incoming shipments. This displacement can take place either laterally, forward or backward.
Another disadvantage is that smaller pieces of mail can drop through an opening that matches the size of the box. The device disclosed in JP-PS 57-48557 is consequently only usable on a limited basis.